We have a NPR diesel with 18' box and will be adding another in few weeks. They work excellent for mowing and saves an incredible amount of labor not having to load and unload 5 times a week. MPG is 9.5-10 WFO for the past 30k miles.

Gotta have a place to pee...I like that.. I run 16 enclosed trailer and having a private place for those most intense time of days, when there are no bushes.. I'm going with a 16ft. box. Nothing like a billboard and garage on wheels.

I recommend a box. keeps all your equipment out of sun and rain and you don't have to unload it every night. I have 2004 isuzu npr hd 20ft box and 4cyl diesel and get around 11.5mpg. Got the valves set and hopefully that will help.